1. Field of the Invention
The present invention relates to an air-conditioning apparatus provided with a compressor.
2. Description of the Related Art
In air-conditioning apparatus, there are cases in which a refrigerant floods a compressor while the apparatus is stopped (hereinafter also referred to as “stagnation”).
The refrigerant that has flooded the compressor dissolves in lubricant oil in the compressor. As a result, the concentration of the lubricant oil is decreased, and the viscosity of the lubricant oil is decreased.
If the compressor is started in this state, the lubricant oil with low viscosity provided to a rotation shaft and a compression portion of the compressor will raise the possibility of a sliding portion and the like in the compressor to be burned due to poor lubrication.
Also, flooding of the refrigerant in the compressor raises the liquid level in the compressor. As a result, start load of an electric motor which drives the compressor becomes higher, which is regarded as an overcurrent at the start of the air-conditioning apparatus, and the air-conditioning apparatus might not be able to be started.
In order to solve these problems, a measure has been taken to suppress refrigerant stagnation in the compressor by heating the compressor while the compressor is stopped.
As heating means to heat the compressor, supply of current to an electric heater wound around the compressor is known. A method of impressing low voltage with high frequency to a coil of the electric motor installed in the compressor without rotating the electric motor, and heating the compressor by Joule heat generated in the coil is also known.
However, because the compressor is heated in order to prevent flooding of the refrigerant in the compressor while the compressor is stopped, electric power is consumed even while the air-conditioning apparatus is stopped.
As a measure against this problem, in conventional technologies, a device that “detects an outside air temperature, changes the time of current applied or the level of voltage applied from an inverter device to a motor coil according to the outside air temperature, and controls so that the temperature of the compressor is kept at a substantially constant value regardless of the change in the outside air temperature” is proposed, for example (see Patent document 1, for example).
Also, a device “provided with saturation temperature calculating means that acquires the saturation temperature of a refrigerant in a compressor on the basis of a detected pressure by pressure detecting means; and control means that compares the acquired saturation temperature and the temperature detected by the temperature detecting means, determines a state in which the refrigerant is easily condensed, and controls the heater so as to heat the compressor when the compressor is stopped and the refrigerant in the compressor is in the state in which the refrigerant is easily condensed” is proposed (see Patent document 2, for example).